1. Field of the Invention
The present invention relates to disk drives. More particularly, the present invention relates to a disk drive that implements a seek operation that utilizes a deceleration velocity profile which mathematically models back electromagnetic forces (BEMFs) associated with an actuator.
2. Description of the Prior Art and Related Information
Today, computers are routinely used both at work and in the home. Computers advantageously enable file sharing, the creation of electronic documents, the use of application specific software, and electronic commerce through Internet and other computer networks. Typically, each computer has a storage peripheral such as a disk drive (e.g. a hard disk drive).
A huge market exists for hard disk drives for mass-market computer systems such as servers, desktop computers, and laptop computers. To be competitive in this market, a hard disk drive should embody a design that is adapted for providing rapid access to data and providing high data storage capacity, while at the same time being energy efficient.
Satisfying these competing constraints of rapid access to data, high data storage capacity, and energy efficiency requires innovation in many of the numerous components of the disk drive.
Further, many newer smaller hard disk drives require reduced power consumption, as well as reduced memory usage, in the processing circuitry of the disk drive itself.
Typically, the main assemblies of a hard disk drive are a head disk assembly (HDA) and a printed circuit board assembly (PCBA). The head disk assembly includes an enclosure including a base and a cover, at least one disk having at least one recording surface, a spindle motor for causing each disk to rotate, and an actuator arrangement. The PCBA generally includes circuitry for processing signals and controlling operations in the disk drive.
An actuator arrangement that is commonly used in hard disk drives is a rotary actuator arrangement included as part of a head stack assembly (HSA) that includes a collection of elements of the head disk assembly. The collection typically includes certain prefabricated subassemblies and certain components that are incorporated into the head disk assembly. For example, a prefabricated head stack assembly (HSA) may include a pivot bearing cartridge, a rotary actuator arrangement, and permanent magnets and an arrangement for supporting the magnets to produce a magnetic field for a voice coil motor.
The rotary actuator arrangement of the HSA may also include a coil forming another part of the voice coil motor, an actuator body having a bore through it, and a plurality of arms projecting parallel to each other and perpendicular to the access of the bore. The rotary actuator arrangement of the HSA may also include head gimbal assemblies (HGAs) that are supported by the arms. Each HGA includes a load beam and a head supported by the load beam. The head is positioned over a track on a recording surface of the disk to write or read data to or from the track, respectively.
Because of the competitive pressure to continually develop hard disk drives that provide faster and more robust access to data, techniques are continuously being developed to decrease the access time to data. One technique to accomplish this is by increasing the speed at which the HSA is pivoted to position the head over a track of the disk in order to access data as part of a seek operation. Particularly, in order to provide faster access to data, techniques are continually being developed to decrease seek time to data.
The seek time generally refers to the time required to move the head of the actuator from a current position or current track to a target position or target track. The seek time is determined by the mechanical characteristics of the HSA and by a seek profile. The seek profile defines, during the time that the actuator is accelerated and decelerated en-route to the target track, a desired acceleration/deceleration profile and desired velocity profile to achieve an efficient and predictable arrival of the head to the target track of the disk.
Disk drive makers work diligently to improve the seek profile and the seek operation. Disk drives now commonly employ velocity profile algorithms as part of their seek operation to efficiently and accurately move the head of the actuator to the target track.
One common problem associated with velocity profile seeking algorithms is the effect of back electromagnetic forces (BEMFs) associated with the coil of the actuator. Previous attempts have been made to account for BEMFs of the coil of the actuator by utilizing look-up tables to approximate how much BEMF is present for a given amount of current applied to the coil. Unfortunately, the use of a look-up table to approximate BEMFs requires a large amount of memory in the circuitry of the disk drive itself.